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title EdgeIdentityTable
parent API Reference

EdgeIdentityTable

Maps a render-path edge ordinal, the value stored in ViewportBody.edgeIndices, back to the Shape it was extracted from, and, when a BRepGraph was supplied, to the durable GraphUID minted from that graph. Mirrors FaceIdentityTable, but for edges.

Why it exists

Unlike the face ordinal, ViewportBody.edgeIndices is already keyed to Shape.edge(at:)'s index space: Shape.edge(at:), the bulk edge-polyline extractor behind ViewportBody.edgeIndices, and Shape.subShapes(ofType: .edge) all build one deduplicating TopTools_IndexedMapOfShape over the shape's edges, so a shared edge between two shells already collapses to a single ordinal there. There is no raw-vs-deduplicated split to reconcile the way there is for faces.

EdgeIdentityTable still earns its keep for the same reasons FaceIdentityTable does: it captures the ordinal to Shape to GraphUID correspondence once, at tessellation time, so a consumer resolving an edge pick does not have to re-walk the shape's edge map itself (Shape.subShape(type:index:) rebuilds it on every call), or hand-roll the graph.findNode(for:) plus graph.uid(ofNodeKind:index:) resolution FaceIdentityTable already does for faces. Edge identity also keeps working even if OCCT's edge traversal ever stopped deduplicating the way it does today.

API

public struct EdgeIdentityTable: Sendable {
    public let shapes: [Shape]
    public let uids: [BRepGraph.GraphUID?]?

    public init(shapes: [Shape], uids: [BRepGraph.GraphUID?]? = nil)
    public func shape(forOrdinal ordinal: Int) -> Shape?
    public func uid(forOrdinal ordinal: Int) -> BRepGraph.GraphUID?
}
  • shapes is indexed by the ordinal stored in ViewportBody.edgeIndices, built from Shape.edges().
  • uids is populated only when a BRepGraph was supplied to the entry point that produced this table. Each element is nil if that ordinal's edge could not be resolved in the graph.
  • shape(forOrdinal:) / uid(forOrdinal:) return nil for an out-of-range ordinal (or, for uid(forOrdinal:), when no graph was supplied at all).

Obtained from CADFileLoader.shapeToBodyMetadataAndIdentities.

Example

let box = Shape.box(width: 10, height: 5, depth: 3)!
let graph = BRepGraph(shape: box)!
let (body, meta, faceTable, edgeTable, vertexTable) = CADFileLoader.shapeToBodyMetadataAndIdentities(
    box, id: "box", color: SIMD4<Float>(0.6, 0.6, 0.65, 1), graph: graph
)
guard let body, let edgeTable else { return }

// Resolve a wireframe edge pick back to its Shape and durable GraphUID.
let pickedOrdinal = Int(body.edgeIndices[0])
let pickedEdge = edgeTable.shape(forOrdinal: pickedOrdinal)
let pickedUID = edgeTable.uid(forOrdinal: pickedOrdinal)